1. Field of the Invention
The present invention relates to an eccentric optical fiber connector ferrule having a desired eccentricity and to the manufacturing method thereof.
2. Description of the Related Art
There is sometimes a need to accurately measure the eccentricity of an optical fiber core of an optical fiber jumper cable, to which a connector is connected, relative to the center of the outside diameter of a ferrule. A connector having a well-known eccentricity amount is used for this purpose. In connection of the optical fiber to the connector, an insertion loss IL (dB) due to an offset d between optical fiber axes is obtained in the following equation in case of a single-mode optical fiber.
IL(dB)=xe2x88x9210logT.exp|xe2x88x92(d/xcfx89)2|
where, T: a transmission loss between the optical fibers
xcfx89: the radius of a mode field of the optical fiber
In this instance, assuming that T=0.93 and xcfx89=4.1 xcexcm, the insertion loss IL (dB) due to the offset d between the optical fiber axes is about 0.1 dB in the case where the offset d of optical axes is 0.5 xcexcm, about 0.23 dB in case of 1 xcexcm, and about 0.9 dB in case of 2 xcexcm.
FIG. 3 shows a graph of the loss due to the offset between the optical fiber axes in connection of the optical fiber connector. It shows that as the offset between the optical fiber axes increase, the variations in loss also increase.
Generally, although the specification of the insertion loss of the jumper cable having the optical fiber ferrule varies depending on the usage and object thereof, almost all are within the range of 0.15 to 0.3 dB.
Assuming that a master connector is eccentric by around 0.3 xcexcm, and the minimum insertion loss when the tested optical fiber ferrule is connected at various angles is 0.3 dB, it is found in FIG. 3 that the distance (the offset amount d) between the center of the master connector core and the center of the tested optical fiber core is around 1.2 xcexcm. Accordingly, the tested optical fiber has the offset of around 1.5 xcexcm. Consequently, the offset d when the tested ferrule is connected to an ideal optical fiber ferrule with the eccentricity of 0 is 1.5 xcexcm, and the insertion loss is approximately 0.5 dB, exceeding the range of the above specifications.
On the other hand, assuming that the insertion loss of the tested optical fiber ferrule when using the master with no eccentricity is 0.2 dB, the offset d is about 0.6 xcexcm; accordingly, even if the same type of optical fiber is connected in the direction in which the offset d is added, the added offset is around 1.2 xcexcM m so that the insertion loss can be maintained within 0.5 dB (d=1.5 xcexcm), ensuring a random connection (non-adjusted connection).
As described above, there is a need to accurately measure the eccentricity of the ferrule core in order to ensure the performance of the jumper cable to which the connector is mounted. The eccentric master optical fiber ferrule having any well-known eccentricity is required for this purpose. Particularly, a need exists for a connector with an eccentric master ferrule in which the eccentricity of 0.1 xcexcm or less can be tested. For this purpose, it is required to determine the amount of the eccentricity of the tested optical fiber ferrule by the variation in the direction of 360xc2x0 and to test the master with small eccentricity using an eccentric master connector in which the core is previously eccentric by 1 xcexcm or more.
The method of manufacturing a conventional eccentric master connector will be briefly described with reference to the following examples.
First, prepare a ferrule with a large central hole, for example, a ferrule with the hole diameter of 130 gm. Insert an optical fiber with the outside diameter of 125 xcexcm therein to form a connector ferrule in which the optical fiber is naturally separated from the central axis thereof. After securing the optical fiber with an adhesive or the like, determine the eccentricity of the optical fiber by observing the end face to measure the eccentricity.
However, it is not easy to manufacture an optical fiber connector ferrule with a specified eccentricity (or a desired amount of eccentricity) by the aforesaid method.
Also, the optical fiber ferrule is sometimes manufactured in a manner in which the optical fiber winds in the central hole of the ferrule in the process of manufacturing the master optical fiber connector ferrule. In general, when measuring a number of tested connector using the master, the end of the master optical fiber connector may be damaged. In such a case, if the defect is removed by polishing the surface of the master connector again, the eccentricity of the ferrule manufactured in the state in which the optical fiber winds may vary, or the master optical fiber axis may incline with respect to the center of the outside diameter of the ferrule.
Referring to FIGS. 4A, 4B, and 4C, the foregoing problems will be described. FIG. 4A is a cross sectional view of the master manufactured in a state in which the optical fiber winds in the central hole of the ferrule, which is exaggeratedly shown for easy understanding. FIG. 4B is a cross sectional view taken on line cxe2x80x94c and FIG. 4C is a cross sectional view taken on line bxe2x80x94b in FIG. 4A. The shape of the cross section when ends of a ferrule 3 and an optical fiber 1 are polished to the position indicated by line bxe2x80x94b is the same (the eccentricity is constant) as that of a view taken on line axe2x80x94a in FIG. 4A; however, the optical axis of an optical fiber core 1A is inclined relative to a center line Oxe2x80x94O of the hole of the ferrule 3. When polishing to a position indicated by line cxe2x80x94c, the eccentricity also varies and the optical axis of the optical fiber core 1A is inclined also relative to the center line Oxe2x80x94O of the hole of the ferrule 3.
When measuring the insertion loss due to the eccentricity of the jumper cable using the eccentric master optical fiber ferrule with the well-known eccentricity, it is required to connect the eccentric master optical fiber ferrule to the tested optical fiber ferrule and to rotate it in the direction of 360xc2x0. In this case, since the optical fiber end of the eccentric master optical fiber ferrule is brought into contact with the ferrule or the optical fiber of the tested optical fiber ferrule and is rotated, defects may be formed at the surface to damage the optical characteristics. When rotating a tested optical fiber ferrule Fe and an eccentric master optical fiber ferrule Fes in a state in which the ends are brought into contact with each other in a sleeve S1 as shown in FIG. 5A, the ends of both optical fibers OF may be damaged.
Accordingly, it is an object of the present invention to provide a stable eccentric ferrule that is parallel to a ferrule-hole axial direction, to which a specified amount (a desired amount) of eccentricity is applied.
It is another object of the present invention to provide a method of manufacturing the eccentric master ferrule with the stable characteristic, to which arbitrary eccentricity is applied.
It is another object of the present invention to provide a stable eccentric ferrule and the manufacturing method in which the shape of an end of the eccentric master optical fiber ferrule is reformed to prevent generation of damage due to the contact and movement relative to a tested optical fiber ferrule.
In order to achieve the above objects, an eccentric optical fiber connector ferrule according to the present invention includes an optical fiber in which a coating at an end thereof is removed to expose the end thereof, a metallic coating bonded to a part of the side face of the optical fiber end in an axial direction, and a ferrule receiving the end of the optical fiber to which the metallic coating is bonded in a central hole thereof, for supporting it while applying a specified eccentricity.
In the eccentric optical fiber connector ferrule, the metallic coating at the side face of the optical fiber end is applied to a part of 1800 or less on the outer periphery of the optical fiber, and the ferrule has a central hole with the outside diameter of the optical fiber plus the thickness of the metallic coating.
In the eccentric optical fiber connector ferrule, the optical fiber end face is recessed from the end of the ferrule within the range of 0.2 to 2.0 xcexcm.
In order to achieve the above objects, a method of manufacturing an eccentric optical fiber connector ferrule according to the present invention includes the steps of removing the coating of the optical fiber and exposing an end of the optical fiber, performing pretreatment of the end of the optical fiber for plating, masking a part of the circumference at the end of the optical fiber except for a part of an arbitrary angle with paint, performing electroless metal plating to the end of the optical fiber so masked, and inserting the end of the optical fiber so metal plated in the central hole of the ferrule for securing.
In the method of manufacturing an eccentric optical fiber connector ferrule, the angle width of the masking is 180xc2x0 or more on the circumference at the side of the optical fiber, and more preferably, a part of around 45 to 90xc2x0 on the circumference is exposed.
In the method of manufacturing an eccentric optical fiber connector ferrule, there is provided the step of previously etching a clad of the optical fiber with an etchant to decrease the clad diameter.
In the method of manufacturing an eccentric optical fiber connector ferrule, there is provided the step of etching a clad of the exposed optical fiber with an etchant after metal plating to decrease the clad diameter.
In the method of manufacturing an eccentric optical fiber connector ferrule, the optical fiber end face is recessed from the end of the ferrule within the range of 0.2 to 2.0 xcexcm by the mechanical or chemical treatment.
In the method of manufacturing an eccentric optical fiber connector ferrule, subsequently to the step of inserting the metal-plated optical fiber end in the central hole of the ferrule for securing, the method further includes the steps of performing an ordinary polishing of end faces of the ferrule and the optical fiber to smooth the end faces of the ferrule and the optical fiber at the center thereof, and recessing the faces so smoothed by buffing or etching with the etchant.